Quick drop valve for bulldozer blade hydraulic controls



June 10, 1969 N. w. KROTH 3,448,685

I QUICK DROP VALVE FOR BULLDOZER BLADE HYDRAULIC CONTROLS Filed Aug. 1,1967 INVENTOR. NEIL W. KROTH ail M, a, W+M

ATTORNEYS United States Patent 3,448,685 QUICK DROP VALVE FOR BULLDOZERBLADE HYDRAULIC CONTROLS Neil W. Kroth, Joliet, Ill., assignor toCaterpillar Tractor Co., Peoria, 111., a corporation of California FiledAug. 1, 1967, Ser. No. 657,669 Int. Cl. F151) 11/10, 13/042; G05d 11/02US. Cl. 91-436 4 Claims ABSTRACT OF THE DISCLOSURE A value associatedwith a double-acting hydraulic jack controlling elevation of a bulldozerblade and permitting rapid extension of the jack and corresponding rapiddescent of the blade to ground level while maintaining adequatehydraulic fluid for driving the blade in further descent to a suitablecutting position. The value has a restricted flow path from the rod endof the jack to drain so that increased fluid pressure acts against aspring loaded spool which communicates the rod end of the jack with thehead end of the jack. As the weight of the blade increases its rate ofdescent toward ground level, a corresponding increased rate of flow offluid from the rod end of the jack moves a sleeve into closing relationwith the fluid flow path through the valve to drain. Thus, a substantialportion of fluid from the rod end of the jack is provided to the headend of the jack.

To increase the operating efiiciency of a bulldozer it is desirable thatthe operator be able to lower the blade to the ground very rapidlywithout the time delay inherent in typical float lowering techniques.Accordingly, bulldozer blades are commonly capable of being freelylowered to ground level under the force of gravity. However, when thelowering of the blade is accompanied by extension of the jack whichcontrols blade elevation, lowering of the blade and extension of thejack by gravity normally results in a time lag of operator control overthe blade since the hydraulic pump associated with the jack is not ofsuflicient capacity to fill the head end of the jack at a correspondingrate. This time lag is undesirable since the operator is unable to forcethe blade below ground level into a suitable cutting position until thehead end of the jack is filled with hydraulic fluid. Undesirable vacuumconditions may also occur within the jack.

The present invention provides a quick drop valve, for employment with ahydraulic motor, which substantially eliminates the undesirable time lagdiscussed above while still permitting rapid operation according togravity.

Use of the quick drop valve is particularly advantageous when employedwith a double-acting hydraulic jack controlling a bulldozer blade sinceit permits the blade to be rapidly lowered toward ground level at aninitial rate determined by the force of gravity. However, as thebulldozer blade approaches ground level and the fluid flow rate from thelower end of the hydraulic jack reaches a preselected level, the quickdrop valve directs most of this fluid to the upper end of the jack sothat the upper end of the jack is filled with fluid and the operator mayimmediately force the bulldozer blade into the ground to a suitablecutting position.

Other advantages and features of the present invention will be apparentfrom the following description and the accompanying drawings, whereinFIG. 1 is a schematic representation of the hydraulic control circuitfor a double-acting hydraulic jack controlling elevation of a bulldozerblade and FIG. 2 is a sectional view of a quick drop valve employedwithin the hydraulic control circuit of FIG. 1 and embodying the presentinvention.

Referring now to FIG. 1, the bulldozer blade 11 is supported uponconventional push arms 12 while its elevation is controlled by a doubleacting hydraulic jack 13. The blade is lowered by extension of a rod 14of the jack while retraction of the rod into the jack serves to raisethe blade. The bulldozer operation positions the blade by manipulating acommon spool-type control valve 16'which directs the flow of hydraulicfluid from a pump 17 through a conduit 18 to a return conduit 19 andtank 21, or alternately to the jack 13. The control valve iscommunicated with the head end of the hydraulic jack by a conduit 22while the rod end of the jack is communicated with the control valvethrough a conduit 23, a quick drop valve 24 and another conduit 26. Thequick drop valve 24 is also communicated with the conduit 22 and thuswith the head end of the jack by another conduit 27. When the operatordesires to raise the blade, he positions the control valve to directfluid from the pump through the conduit 26, the quick drop valve and theconduit 23 to the rod end of the hydraulic jack while the head end ofthe jack is communicated to drain by the conduit 22, the control valveand the conduit 19. To lower the blade, the operator positions thecontrol valve spool to direct fluid to the head end of the jack throughthe conduit 22 while the rod end of the jack is communicated to drainthrough the conduit 23, the quick drop valve, the conduit 26, thecontrol valve and the conduit 19.

To briefly summarize the quick drop valve of the present invention,having reference also to FIG. 2, the quick drop valve 24 hassubstantially no eflect on fluid flow when the bulldozer blade is beingraised, but rather is effective when the operator positions the controlvalve to lower the bulldozer blade by extension of the hydraulic jack13. During lowering of the bulldozer blade, a fluid flow path from therod end of the jack to drain is provided by a passage 28 within thequick drop valve. The passage 28 has a restriction or orifice 29 whichdoes not substantially eflect the rate of flow of fluid through thepassage but which creates a pressure differential across the quick dropvalve with the conduit 23 representing the high pressure side and theconduit 26 representing the low pressure side thereof. The relativelyhigh pressure hydraulic fluid in the quick drop valve adjacent theconduit 23 acts against a spring-loaded valve 31 and causes it to placethe conduit 23 in fluid communication with the conduit 27 and the headend of the jack. As the rate of fluid flow from the rod end of the jackthrough the conduit 23 and the quick drop valve to drain reaches a levelindicating that the blade is approaching ground level, variable valvemeans 32 respond to that rate of flow by limiting fluid flow into thepassage 28 so that a substantial portion of the fluid from the rod endof the jack is directed to the head end of the jack through the quickdrop valve and the conduit 27. Thus, the present quick drop valve isdoubly advantageous since it initially permits the bulldozer blade to belowered at a rate substantially determined only by the force of gravity.However, as the bulldozer blade approaches ground level, the fluid fromthe rod end of the jack is directed to the head end of the jack toassist the pump 17 in filling the head end of the jack with fluid. Thus,the quick drop valve of the present invention permits the operator toimmediately force the bulldozer blade below ground level into a suitablecutting position by means of the hydraulic jack.

To describe the quick drop valve in structural detail, it has a centralbore 33 with the spring-loaded valve 31 comprising a spool 34 disposedfor longitudinal motion in the bore and urged leftwardly into theposition illustrated in FIG. 2 by a spring 36. The conduit 23 iscommunicated directly into the left end of the spool bore 33 while thespool bore is communicated with one end of the passage 28 by means of anannular recess 37. The other end of the passage 28 is in communicationwith the conduit 26. The spool bore is also in communication with theconduit 27 by means of an annular recess 38 and a passage 39. Thespring-loaded spool is recessed at its left end and has radial ports 41which communicate the recessed left end of the spool with the annularrecess 37 when the spool is leftwardly disposed in the bore 33. When theabovenoted differential pressure exists within the quick drop valve, itdrives spool 34 rightwardly against the spring 36 so that the ports 41are in communication with the annular recess 38 as well as the annularrecess 37. At this point, the flow path of fluid from the conduit 23 isstill substantially through the passage 28 since it represents a freepath to drain.

To insure that a substantial portion of the fluid flow from the rod endof the hydraulic jack passes to the head end of the hydraulic jack atleast when the blade is approaching ground level, the recessed left endof the spool 34 has a counterbore 42 which is only partially coextensivewith the ports 41 in the spool. The variable valve means 32 comprises asleeve 43 which is slidably disposed in the counterbore 42 forcooperation with the ports 41. When the fluid flow rate from the conduit23 into the quick drop valve reaches a rate indicating that thebulldozer blade is descending and approaching ground level, the slidablesleeve 43 is carried rightwardly by the fluid flow from the conduit 23so that it abuts the right end of the counterbore 42. In this position,the sleeve limits fluid flow to the passage 28 by permitting fluid toflow only through that portion of the port 41 which is not coextensivewith the counter bore 42. A substantial portion of the fluid flows fromthe rod end of the jack thus through the annular recess 38, the passage39, the conduit 27 and the conduit 22 and assists the pump 17 in fillingthe head end of the hydraulic jack to prevent any time lag in operatorcontrol over the bulldozer blade through the jack. The sizing of thecomponents within the quick drop valve is such as to divided fluid flowfrom conduit 23 between the conduit 27 and the passage 28 at a ratio of,for example, 80 to 20. Some fluid flow is always directed back to drainthrough the restricted passage 28 in order to maintain the pressuredifferential necessary to hold the spool 34 in its extreme rightposition within the spool bore 33 It is also to be noted that when thebulldozer blade is being raised and fluid flow passes through the quickdrop valve from the conduit 26 to the conduit 23, the pressuredifferential resulting within the valve according to the orifice 29 willnot effect the position of the spool 34 since the spool is then on thelow pressure side of the orifice. Thus, the spool remains in its extremeleft position according to interaction with the spring 26.

If it is desired to operate the control system so that the blade dropscompletely to ground level under the force of gravity, the sleeve 43 mayreadily be removed from the quick drop valve and fluid flow from the rodend of the jack to drain through the passage 28 will not be limited evenwith a high rate of fluid flow through the quick drop valve.

What is claimed is:

1. A quick drop valve in association with a hydraulic control circuit ofa double-acting hydraulic motor which is capable of operating under theforce of gravity with hydraulic fluid accordingly expelled from a firstchamber of the motor while fluid is provided by a pump to a secondchamber of the motor, the combination comprising a housing defining abore in effective communication with the two motor chambers and aconduit having a restrictive orifice for communicating the bore to drainand causing relatively high fluid pressure in the bore when fluid isexpelled from the first motor chamber,

a valve spool reciprocably mounted in the bore and normally positionedby a spring to communicate the first motor chamber only with therestricted conduit, the spool being capable of shifting against itsspring in response to the relatively high pressure fluid, and

variable valve means eflectively formed as a portion of the valve spoolto direct a portion of the fluid from the first motor chamber to thesecond chamber when the spool is shifted against its spring,

a control valve disposed in the circuit to communicate fluid from a pumpwith the second motor chamber of the motor by a first conduit, 7

a second conduit communicates the first motor chamber of the motor withthe valve bore,

a third conduit communicates the restricted passage with the controlvalve, and

a fourth conduit communicates the first conduit with the valve bore, thevariable valve means being effective to communicate the second conduitwith the fourth conduit when the spool is shifted against its spring.

2. A quick drop valve in association with a hydraulic control circuit ofa double-acting hydraulic motor which is capable of operating under theforce of gravity with hydraulic fluid accordingly expelled from a firstchamber of the motor while fluid is provided by a pump to a secondchamber of the motor, combination comprising a housing defining a borein effective communication with the two motor chambers and a conduithaving a restrictive orifice for communicating the bore to drain andcausing relatively high fluid pressure in the bore when fluid isexpelled from the first motor chamber,

a valve spool reciprocably mounted in the bore and normally positionedby a spring to communicate the first motor chamber only with therestricted conduit, the spool being capable of shifting against itsspring in response to the relatively high pressure fluid, and

variable valve means effectively formed as a portion of the valve spoolto direct a portion of the fluid from the first motor chamber to thesecond chamber when the spool is shifted against its spring.

the valve bore having a first annular recess in communication with oneend of the restricted passage and a second annular recess incommunication with with the second motor chamber, the spool having atleast one port formed by a tubular portion thereof, the port being inselective communication with the two bore recesses according to theposition of the spool within its bore.

3. The combination of claim 2 wherein the variable valve means comprisesa slidable sleeve disposed in a counterbore of the tubular portion ofsaid spool, said counterbore permitting said sleeve to be shifted by apreselected rate of fluid flow from the first motor chamber into thevalve and block a portion of said port in the tubular portion of thespool.

4. The combination of claim 3 wherein the quick drop valve is effectiveto permit substantially unimpeded fluid flow from first motor sidetherethrough the drain except upon operation of said variable valvesleeve,

the tubular portion of the spool comprises a plurality of said ports andthe slidable valve sleeve is removable from the quick drop valve.

(References on following page) References Cited 3,241,461

UNITED STATES PATENTS 1/1945 Kehle 91-436 7/1953 Deardorif 9'1-43610/1961 Ruhl 91-436X 5 137-101 3/1966 Drone 91-436 CARROLL B. DORITY,IR., Primary Examiner.

US. Cl. X.R.

